Microbial pre-treatment of double refractory gold ores

ABSTRACT

The present invention is directed to recovery of gold from refractory and double refractory ores using a fungal agent and/or culture media.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims the benefits of U.S. ProvisionalApplication Ser. Nos. 60/990,805, filed Nov. 28, 2007, and 61/088,928,filed Aug. 14, 2008, both entitled “Microbial Pre-Treatment of DoubleRefractory Gold Ores”, both of which are incorporated herein by thisreference in their entireties.

FIELD

The invention relates generally to hydrometallurgical gold recoveryprocesses and particularly to biological processes for recovering goldfrom refractory and double refractory materials.

BACKGROUND

In carbonaceous gold bearing ores, preg robbing occurs when activecarbon, indigenous to the ore, complexes with the gold dissolved incyanide leach solutions, thereby reducing gold recovery. “Preg robbing”is a generic term and can refer to any of several phenomenon related toan ore's Total Carbonaceous Material (TCM). Not only can preg robbing becaused by activated carbon, but also it can be caused either by highmolecular weight hydrocarbons usually associated with the activatedcarbon or by organic acids, such as humic acid, having functional groupscapable of interacting with gold complexes to form organic goldcompounds. (P. Afenya, Treatment of Carbonaceous Refractory Gold Ores,Minerals Engineering, Vol. 4, pp. 1043-1055, 1991. W. Guay, TheTreatment of Refractory Gold Ores Containing Carbonaceous Material andSulfides, Society of Mining Engineers of AIME, 81-34, pp. 1-4, 1981). Anadditional problem in recovering gold from highly carbonaceous ores isthat a significant quantity of the gold may have been adsorbed ontocarbon during formation of the mineral deposit. Cyanide has shownvarying degrees of success in leaching gold locked in carbonaceousmaterial.

Many gold deposits currently processed throughout the world are sulfidicin nature and may contain the gold in a form that is inaccessible tolixiviants. Gold is frequently present in these ores as very finelydisseminated particles encapsulated by a sulfide mineral structure. Theinaccessibility of the gold to the lixiviant has been overcome byoxidizing the sulfides contained in the ore, thereby liberating goldparticles from the sulfide matrix and rendering the gold amenable tocyanidation. Some ores are characterized as double refractory becausethey are both sulfide refractory and preg robbing carbonaceousrefractory.

Several approaches to reduce the impact of carbonaceous preg robbing insulfide ores have been employed with varying degrees of successdepending on the feed ore's refractory and mineralogicalcharacteristics. These methods include; flotation, the addition ofblanking agents, competitive loading onto commercial activated carbon,roasting, chemical oxidation and bioleaching.

Flotation is most successful when a small proportion of gold isassociated with the preg robbing carbonaceous matter in the ore. Thecarbonaceous matter is floated off and discarded. The remaining ore isthen processed using conventional cyanidation techniques. Thistechnique, however, does not work for ores in which considerablequantities of gold are associated with the carbonaceous component.

The addition of blanking agents, such as kerosene, fuel oil, and RV-2(para nitro benzol azo salicylic acid), adsorb selectively onto thesurface of activated carbon in carbonaceous ores, thereby deactivatingsome of the preg robbing character. Fuel oils exhibit a high affinityfor carbonaceous material, particularly graphitic carbon, and adhere tohydrophobic surfaces of carbonaceous matter, thereby reducing itsadsorptive capacity. Because fuel oil is lighter than water it will notseparate readily from the ore solids in the slurry after leaching. Thisentrainment causes problems in subsequent operations, particularlyliquid solid separation.

Carbonaceous matter can also be destroyed by roasting. This is thecurrent industry standard for simultaneously destroying the carbonaceousmatter while oxidizing sulfide minerals in double refractory gold ores.This process is generally, but not always, successful and depends uponthe temperature of roasting. Very high temperatures are often requiredto combust some preg robbing carbon species. Roasting plants operate ina narrow range of temperature tolerance. Below optimum temperature, thecarbon in the ore is not oxidized and remains actively preg robbing.Above the optimum temperature, the gold in the ore becomes increasinglyless amenable to cyanidation or other extraction techniques. Because ofthe degrading gold recovery with higher roasting temperatures, manyroasters are operated toward the lower side of the temperature range.Roaster efficiency in a plant environment tends to vary widely withvariation in feed stock. Roasting may not be suitable or economical forores that contain low levels of sulfide and high levels of carbonates,because the roasting is not autogenous

Activated carbon or resin can be added to leach solutions topreferentially adsorb gold-cyanide. This process depends on theadsorbent having a stronger affinity for gold than the than thecarbonaceous matter in the ore. This process is not effective when theore contains large amounts of carbonaceous matter. It has also been beenreported that native carbonaceous matter has the ability to adsorb thegold cyanide complex four times faster than activated carbon. (B. J.Scheiner, Relation of Mineralogy to Treatment Methods for CarbonaceousGold Ores, Society of Mining Engineers, 87-96, pp 1-6, 1987).

U.S. Pat. No. 5,536,480 discloses a method for pressure oxidizingcarbonaceous refractory ores. The method employs a combination of veryfine sizing of the ore feed with severe pressure oxidation processing tooxidize and/or passivate the preg robbing organic carbonaceous material.Although pressure oxidation can partially deactivate the indigenouscarbon, it is often unable to deactivate the preg robbing carbon inhighly preg robbing ores. Surprisingly, pressure oxidation has beenshown, in some instances, to activate carbonaceous matter.

U.S. Pat. No. 4,729,788 employs bio-oxidation to treat double refractorysulfide and carbonaceous gold ores. The process uses bacteria tobiologically degrade sulfide minerals and liberate precious metal valuesso that they can be recovered by conventional technologies. The mostwidely used and studied bacteria for this process is Acidithiobacillusferrooxidans. As bio-oxidation has little effect on the preg robbingcharacteristics of an ore, a blinding agent, such as “Actinol FA1” (aform of Toll Oil), is used to bind the preg robbing carbon to obtainsatisfactory gold yields from carbonaceous ores.

U.S. Pat. Nos. 5,244,493 and 5,127,942 disclose a process for treatingdouble refractory ores in which bio-oxidation of sulfidic minerals isfollowed by microbial treatment to reduce the effects of preg robbingcarbon. This treatment uses a consortium of bacterial comprising atleast two bacteria selected from the group consisting of Pseudomonasmaltophilia, Pseudomonas oryzihabitans, Pseudomonas putida, Pseudomonasfluorescens, Pseudomonas stutzeri, Achromobacter species, Arthrobacterspecies, and Rhodococcus species. The blanking agent disclosed in thispatent is a product of the above microbial consortium (column 2, line17). The disadvantage of this patent is that the deactivation of pregrobbing carbon is facilitated by addition of a chelating agent at veryhigh dosages. The preferred dosage range quoted, 0.5 g to 5 g EDTA/20 gof ore or 25-250 kg EDTA per tonne of ore, is likely to be economicallyprohibitive.

There is therefore a need for an economical and practical method totreat the preg robbing component of single or double refractory ore.

SUMMARY

These and other needs are addressed by the various embodiments andconfigurations of the present invention. The present invention isdirected generally to the recovery of gold and other precious metalsfrom refractory and double refractory materials using bio-active agents,particularly fungal agents.

In a first embodiment, a method is provided for treating refractory anddouble refractory gold-containing materials containing preg robbingcarbon-containing components using a fungal agent to deactivate the pregrobbing components. The fungal agent can be any suitable fungus,including a white rot fungus, with any Coriolaceae cellular organismbeing preferred and any Trametes cellular organism, such as Trametesversicolor (formerly Coriolus versicolor), being even more preferred.Before or after inoculation by the fungal agent, any refractory sulfidesulfur may be oxidized by a suitable technique, including roasting,atmospheric oxidation, pressure oxidation, and bio-oxidation. Thisembodiment can provide an economical and practical method to treat notonly refractory but also double refractory ores.

In a second embodiment, a method is provided for treating refractory anddouble refractory gold-containing materials containing sulfidic sulfurusing a fungal agent to decompose sulfides. The fungal agent can be anysuitable fungus, including a white rot fungus, with any Coriolaceaecellular organism being preferred and any Trametes cellular organism,such as Trametes versicolor (formerly Coriolus versicolor), being evenmore preferred. Before or after inoculation by the fungal agent, anypreg robbing carbon-containing components may be deactivated by asuitable technique. One preferred technique is bio-deactivation usingfungal and/or bacterial microbes.

In a third embodiment, a method is provided for treating refractory anddouble refractory gold-containing sulfidic materials. A culture media,with or without a microbial agent, is applied at elevated temperature tothe material to oxidize sulfidic sulfur. The culture media may be for amicrobe that deactivates preg robbing carbon-containing material. Inthat event, the gold-containing material may be inoculated with themicrobe during or after sulfidic sulfur oxidation.

The second and third embodiments can oxidize sulfidic sulfur at analkaline pH, thereby reducing base consumption compared to bacterialoxidation of sulfidic sulfur.

These and other advantages will be apparent from the disclosure of theinvention(s) contained herein.

As used herein, “a” or “an” entity refers to one or more of that entity.As such, the terms “a” (or “an”), “one or more” and “at least one” canbe used interchangeably herein. It is also to be noted that the terms“comprising”, “including”, and “having” can be used interchangeably.

As used herein, “acid consumer” refers to any material that reacts withsulfuric acid to form a new compound. Specific examples of acidconsumers include carbonates, such as limestone, soda ash, trona,ankerite, dolomite, and calcite; alkaline earth metal oxides such aslime; other metal oxides such as zinc oxide and magnesium oxide; alkalimetal hydroxides such as sodium hydroxide and potassium hydroxide; othermetal hydroxides such as ferric hydroxide (e.g., limonite and goethite)and aluminum hydroxides such as laterite, gibbsite, and diaspore;ammonia; and various clays.

As used herein, “at least one”, “one or more”, and “and/or” areopen-ended expressions that are both conjunctive and disjunctive inoperation. For example, each of the expressions “at least one of A, Band C”, “at least one of A, B, or C”, “one or more of A, B, and C”, “oneor more of A, B, or C” and “A, B, and/or C” means A alone, B alone, Calone, A and B together, A and C together, B and C together, or A, B andC together.

As used herein, “carbonaceous material” refers to organiccarbon-containing material. Examples of organic carbonaceous materialsinclude humic acid, hydrocarbons, and naturally occurring activatedcarbon.

As used herein, “deactivation” refers to decomposition or alteration,such as by oxidation and/or reduction, of a selected chemical compoundand/or passivation of a selected material.

As used herein, “malt” refers to grains that have been partiallygerminated by artificial means. Malt normally contains dextrin, maltose,and amylase.

As used herein, “passivate” means to form a coating on a surface andreduce a selected chemical activity or function.

As used herein, “yeast” refers to unicellular organisms known assaccharomycetaceae.

The preceding is a simplified summary of the invention to provide anunderstanding of some aspects of the invention. This summary is neitheran extensive nor exhaustive overview of the invention and its variousembodiments. It is intended neither to identify key or critical elementsof the invention nor to delineate the scope of the invention but topresent selected concepts of the invention in a simplified form as anintroduction to the more detailed description presented below. As willbe appreciated, other embodiments of the invention are possibleutilizing, alone or in combination, one or more of the features setforth above or described in detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are incorporated into and form a part of thespecification to illustrate several examples of the presentinvention(s). These drawings, together with the description, explain theprinciples of the invention(s). The drawings simply illustrate preferredand alternative examples of how the invention(s) can be made and usedand are not to be construed as limiting the invention(s) to only theillustrated and described examples. Further features and advantages willbecome apparent from the following, more detailed, description of thevarious embodiments of the invention(s), as illustrated by the drawingsreferenced below.

FIG. 1A is a flowsheet of a process according to an embodiment; and

FIG. 1B is a flowsheet continuation of the process of the embodiment.

DETAILED DESCRIPTION

Refractory carbonaceous material is contacted with a heterotrophicbio-active agent, particularly a fungal agent, to deactivate pregrobbing carbonaceous components. Although any suitable fungi may beemployed, a preferred heterotrophic agent is an Aphyllophorales cellularorganism, more preferably a Coriolaceae cellular organism, even morepreferably white rot fungi and mutants thereof, with a Trametes cellularorganism (e.g., Trametes trogii, Trametes hirsuta, and Trametesversicolor (formerly Coriolus sp.)), a Phanerochaete cellular organism(e.g., Phanerochaete chrysosporium and Phanerochaete sordida), aBjerkandera cellular organism, a Phlebia cellular organism (e.g.,Phlebia brevispora), a Cyathus cellular organism (e.g., Cyathusstercoreous), and a Tyromyces cellular organism (e.g., Tyromycespalustris) and mutants thereof being even more preferred and a Trametesspecies and mutants thereof being even more preferred. In oneconfiguration, the bio-active agent can not only deactivate carbonaceouscomponents but also oxidize sulfide minerals. These fungi are commonlyactive at temperatures in the range of about 15 to about 45° C. and at apH of at least about pH 3, even more commonly in the range of about pH 5to about pH 12, and even more commonly in the range of about pH 8 toabout pH 10.

While not wishing to be bound by any theory, the fungi are believed tosecrete a number of enzymes, particularly peroxidases and laccases withunique properties. The enzymes can catalyze a wide variety of oxidationsand both indirect oxidations and reductions. The fungi synthesize andsecrete hydrogen peroxide to activate the peroxidases and laccases,veratryl alcohol to serve as a free radical intermediate for indirectoxidations, and/or electron donors, such as oxalate, which, withveratryl alcohol, catalyze reductions. Reductions are often required forsubsequent oxidation of chemicals by the peroxidases and laccases. It isbelieved that some carbonaceous materials are converted into carbondioxide by some fungi while other fingi passivate the pre-robbingcapacity of carbonaceous materials.

A process according to a first embodiment will be discussed withreference to FIGS. 1A and 1B. The process oxidizes sulfides andbio-deactivates carbonaceous components in different stages and bydifferent means.

A feed material 100 contains gold and can be in any suitable form, suchas ore, concentrate, tailings, calcine, and residue of an extractivemetallurgical process. The gold content of the feed material 100 dependson the form of the material and typically ranges from 0.1 to about 5.0oz/tonne and even more typically from about 0.2 to about 2 oz/tonne. Thematerial 100 includes a preg robbing carbonaceous component, such ashumic acid, hydrocarbons, and surface active carbon, in an amountranging from about 0.3 to about 10 wt. %. The material 100 can alsoinclude other components, including one or more of silver in an amounttypically ranging from about 1 to about 10 oz/tonne and even moretypically ranging from about 1 to about 5 oz/tonne, sulfidic sulfur inan amount typically ranging from about 0.1 to about 15 wt. %, and acidconsumers in an amount typically ranging from about 0.1 to about 30 wt.%. Depending on the mineralogy of the material, the sulfide minerals arecommonly in the form of pyrite, marcasite, arsenopyrite, andchalcophyrite while the acid consumers are commonly present ascarbonates, ankerite, calcite, siderite, and dolomite.

The particle size of the feed material 100 depends on subsequentprocessing steps and mineralogy. For example, when the feed material 100particles will be bio-treated in a vat or other container the P₈₀ sizeof the material will be minus 75 μm. Commonly, the feed material 100will have a median, average, and/or P₈₀ size in the range of from about10 μm to about 25 mm.

Optional steps 104, 108 and 112 are performed, when the feed material100 is sulfide refractory, to oxidize sulfidic sulfur sufficiently toliberate most of the gold from the sulfide matrix. Sulfide oxidation maybe performed by any technique, including alkaline or acid atmospheric orpressure oxidation, roasting, and bio-oxidation. Preferably, oxidationis performed by bio-oxidation in a tank. In bio-oxidation, the material100 is inoculated with a chemolithotrophic autotrophic bacterialconsortium, typically including Acidithiobacillus ferrooxidans,Acidithiobacillus thiooxidans and Leptospirillum ferrooxidans.Alternately or additionally, the bacteria used for oxidative leachingcomprise at least one bacteria selected from the group consisting ofThiobacillus thiooxidans, Acidithiobacillus ferrooxidans, aLeptosoirillum species, Thermosulfidooxidans, Sulfolobus brierleyi,Sulfolobus acidocaldarius, Sulfolobus BC and Sulfolobus solfataricus.Thiobacillus ferrooxidans bacteria are suitable for sulfide oxidationwithin the temperature range of about 15 to about 40° C. Thefacultative-thermophilic iron-oxidizing bacteria oxidize sulfides at atemperature range of about 35 to about 55° C. The Sulfolobus andAcidianus species are active from about 50 to about 90° C.

The various reactions occurring during bio-oxidation are believed to be:

2FeS_(x)+7O₂+2H₂O→xFeSO₄+xH₂O  (1)

4FeSO₄+O₂+2H₂SO₄→2Fe(SO₄)₃+2H₂O  (2)

FeS_(x)+Fe₂(SO₄)₃→3FeSO₄+xS  (3)

2S+3O₂+2H₂O→2H₂SO₄  (4)

Reactions (1) and (3) are believed to be mainly chemical reactions andoccur with little or no bacterial involvement. Reactions (2) and (4) arebelieved to rely entirely on bacterial catalysis and will not proceed toany appreciable degree in the absence of active bacteria under ambientconditions. The final oxidation products of sulfide minerals should beferric sulfate and sulfuric acid.

Sulfide bio-oxidation takes place at a pH of less than about pH 2.5,with an operable range being from about pH 1.3 to about pH 2.0. Toattain or maintain this pH, the material 100 may need to be contacted,before bio-oxidation, with an acid to destroy acid consumers.

To promote microbial activity, nutrients, such as soluble Fe³⁺; ammoniumsulfate, and phosphate, are contacted with the material 100, during andafter inoculation. Bio-oxidation is further discussed in U.S. Pat. Nos.4,729,788, 5,089,412, 5,127,942, and 6,696,283.

Sulfide bio-oxidation may be carried out prior to or subsequent to thecarbon deactivation by the bio-active (fungal) agent disclosed herein.In some cases, this reversal of steps is desirable to prevent liberatedgold from being lost to preg robbing carbon before the preg robbingcarbon is deactivated.

Through oxidation, commonly 25% or more, even more commonly more than50%, and even more commonly 85% of the sulfidic sulfur in the feedmaterial 100 is oxidized in step 104.

The oxidized residue 116, when in the form of a slurry, is subjected tosolid/liquid separation in step 108, such as using a counter currentdecantation circuit, to produce a separated residue 120. The oxidizedand separated residue 116 and 120, respectively, contain most of thegold. The liquid component may be recycled to step 104.

In step 112, the residue is washed in a wash circuit to reduce acidlevels, remove bacteria, and form a washed residue 124.

In step 128, the residue 124, which is typically in the form of aslurry, is neutralized, as needed, using base 136 to produce the desiredpH range (discussed above), conditioned to produce a desired pulpdensity, and inoculated. The base 136 can be any acid consumer, such aslime and limestone, with lime being preferred. The pulp density isadjusted with solution from step 132 to a preferred range of about 10 toabout 50% and even more preferably of about 20 to about 30%.

The bio-active (fungal) agent 140, commonly in the form of an inoculantor culture media, are contacted with the neutralized and conditionedslurry during step 128 and/or during bio-treatment step 152. Theinoculant preferably contains from about 10⁵ to about 10⁸ colony-formingunits per milliliter, preferably as a suspension in a nutrient solution.Preferably, the colony forming units are grown for a suitable period ona culture medium before inoculation. Commonly, the bio-active agent 140does not include heterotrophic carbon deactivating bacteria, such asPseudomonas maltophilia, Pseudomonas oryzihabitans, Pseudomonas putida,Pseudomonas fluorescens, Pseudomonas stutzeri, Streptomyces setonii,Arthrobacter species, Achromobacter species, and Rhodococcus species.

The inoculant or culture media includes nutrients 144 to promote growthand reproduction of the bio-active agent. Nutrients generally include acarbon source and one or more inducers to encourage or enhanceproduction by the bio-active agent of one or more selected enzymes thateffect the desired deactivation of the preg robbing carbonaceousmaterials. In one formulation, the nutrients 144 are aglucose-malt-yeast extract medium preferably including, in each liter ofnutrient solution, from about 5 to about 50 g/L glucose, from about 1 toabout 25 g/L malt extract, from about 0.5 to about 25 g/L yeast extract,and from about 0.1 to about 10 g/L of an alkaline earth metal sulfate,particularly hydrated magnesium sulfate, with the remainder of thesolution being (preferably distilled) water. In another formulation, thenutrient-containing solution is an aqueous mixture including from about10 to about 20 parts Kirk's medium, from about 1 to about 1.5 partspolysaccharide (e.g., a phycocolloiod, particularly agar (which is amixture of agarose and agaropectin)) and from about 2.5 to about 3 partsmalt extract or maltine, with the remainder being (preferably distilled)water. One liter of Kirk's medium preferably includes about 10 gramsglucose or dextrose, from about 0.44 to about 0.80 grams ammoniumtartrate, about 0.05 gram of a transition metal sulfate, particularlyhydrated manganese sulfate, about 0.1 gram of an alkaline earth metalchloride, particularly hydrated calcium chloride, about 100 μmlthiamine, about 100 μml trace minerals, and about 3 gram 2.2dimethylsucicinate supplement. Unlike U.S. Pat. No. 5,244,493, theinoculating solution or culture media excludes, and bio-treatment step152 is performed in the complete or substantial absence of, a chelatingagent, particularly ethylene diamine tetraacetic acid.

The conditioned material 148 is bio-treated in step 152 to deactivatemost and even more preferably from about 75 to about 95% of the pregrobbing carbonaceous material. During bio-treatment, nutrients 144 and,as needed, additional bio-active agent 140, are contacted with theconditioned material 148. While not wishing to be bound by any theory,the bio-active agent, using the particles of conditioned material 148 asa substrate, metabolizes, multiplies, and produces biomass. During thegrowth process, the fungus is believed to attach to the carbonaceouscomponents of the conditioned material 148. Fungal deactivation ofcarbonaceous components to a non-preg robbing form is believed to resultfrom coating the carbonaceous components with the fungal-producedbiomass. The biomass may block or “blind” the carbonaceous material fromreacting with dissolved gold.

To maintain desired growth and reproductive rates of the bio-activeagent, further inoculations of the bio-active agent and nutrientsolution are done during bio-treatment. This can be done either on acontinuous or discontinuous basis. The pulp density is preferablymaintained in the range set forth above.

Typically, neutralization/conditioning and bio-treatment will take placein a series of vessels, such as tanks, columns, or vats. The vessels arepreferably continuous or semi-continuous stirred tank vessels. Commonly,the series includes a neutralization/conditioning vessel followed by oneor more reactor vessels (in which bio-treatment occurs).

Molecular oxygen is generally provided to support fungal growth.Molecular oxygen is commonly provided by sparging air through theneutralization/conditioning and/or bio-treatment vessels.

The residence time is the time required to substantially reduce, ordeactivate, the preg robbing characteristic of the ore and commonlydepends on the characteristics of the conditioned material 148 andprocessing conditions, such as feed rate, temperature, particle size,and pulp density. The residence time of the conditioned material 148 inthe reactor tank(s) typically ranges from about one to about 3 weeks.

The bio-treated material 156 includes most, if not all, of the gold inthe feed material 100.

In optional step 132, the bio-treated material 156, which is in the formof a slurry, is subjected to solid/liquid separation, such as in acounter current decantation circuit, to separate a portion of the liquidphase from the solid phase (or bio-treated material 156).

In optional step 160, the separated bio-treated material 156 isneutralized using a suitable base 136. The base 136 is preferably lime.

The neutralized bio-treated material 164, in step 168, is leached usinga lixiviant to form a pregnant leach solution 172 containing most of thegold in the material 164 and a barren material 176. The lixiviant can beany suitable gold-dissolving leaching agent, such as cyanide,thiosulfate, or thiourea, with cyanide being preferred.

In step 180, dissolved gold in the pregnant leach solution 172 isrecovered by suitable techniques to form a gold product 184. Goldrecovery and leaching can be performed sequentially or simultaneously.In a preferred configuration, dissolved gold is concentrated byadsorption onto activated carbon either in adsorption columns, in carbonadded to the leaching process (known as Carbon-In-Leach (“CIL”) orCarbon-In-Pulp (“CIP”) techniques), or in resin added to the leachingprocess (known as Resin-In-Leach (“RIL”) technique). Adsorbed gold iseluted from the sorbent by stripping with ammonia, nitric acid, caustic,steam and/or other stripping solutions. Gold is then isolated andconverted to a solid from the eluate by electrowinning (electroplatingof gold onto cathodes), precipitation and filtration, or cementation.

In step 188, the barren material 176 is subjected to solid/liquidseparation to form tailings 192, which may be discharged into a tailingspond or otherwise disposed of.

Because treatment of feed material 100 with a bio-oxidizing consortiumoccurs at an acid pH and cyanidation of the bio-treated material 156occurs at an alkaline pH, it is desirable, after bio-oxidation (step104) and before bio-treatment of carbonaceous components andcyanidation, to raise the pH of the oxidized residue 116 into thealkaline regime. It is, however, possible to bio-treat the carbonaceouscomponents before sulfide oxidation (step 104). This configuration ispractical when the ore contains a high amount of carbonate and otheracid consumers and is subjected to alkaline pressure oxidation. As willbe appreciated, in alkaline pressure oxidation the autoclave dischargehas a neutral to alkaline pH as described by Mason in U.S. Pat. No.4,979,987.

In one alternative embodiment, the feed material 100 is processed byheap leaching techniques. The feed material 100 is comminuted to acoarse size and/or formed into aggomerates. In heap leaching, theparticles of feed material 100, for example, typically have a P₉₀ sizeof less than about 2 inches and even more typically less than about 0.5inches. The heap is inoculated with, and sprayed with nutrients for, thechemolithotrophic bacteria. When sulfide oxidation is at a selecteddegree of completion, the heap is dismantled and theparticles/agglomerates neutralized with soda ash or limestone. Theneutralized particles/agglomerates are reformed into a heap andbio-treatment performed to deactivate the preg robbing carboncomponents. When bio-treatment is at a selected degree of completion,the heap, if necessary, is dismantled and the particles/agglomeratesneutralized with lime. The heap is reformed again. The gold is recoveredby contacting the heap with an alkaline lixiviant, such as cyanide,thiosulfate, and thiourea.

In another embodiment, sulfide oxidation is effected at elevatedtemperature using a nutrient-containing solution or culture media in thesubstantial absence of a fungal or bacterial agent. The microbe-barrennutrient solution is contacted with the feed material 100 in a stirredtank for a time sufficient to oxidize a substantial portion of thesulfides. The contacting temperature is typically about 30° C. or higherand even more typically ranges from about 40 to about 45° C. and the pHis about pH 9 or more and even more typically ranges from about pH 9.5to about pH 10.5. The nutrient solution can have the composition setforth above in connection with fungal agents. As will be appreciated,the byproducts of sulfide oxidation (e.g., sulfuric acid) may cause thepH of the culture media to decrease during the course of sulfideoxidation. Consequently, base is added, as needed, to maintain the pH ofthe culture media at the desired level. Before or after oxidation, pregrobbing carbon-containing component deactivation by fungal or bacterialmicrobes is effected as set forth above.

In another alternative embodiment, the sulfide destruction capability ofthe bio-active agent 140 and the oxidative ability of the nutrientsolution are jointly used to effect bio-oxidation (step 104). It is wellestablished that white rot fungus decomposes dibenzyl sulfide todibenzyl sulfoxide and/or dibenzyl sulfone. Van Hamme, Dibenzyl SulfideMetabolism by White Rot Fungi, Applied and Environmental Microbiology,February 2003, pages 1320 to 1324 (2003). Accordingly, white rot fungusand the nutrient solution are applied, together or separately, to thefeed material 100, either by heap or tank leaching techniques, todecompose commonly at least about 25 wt. %, even more commonly more thanabout 50 wt. %, and even more commonly at least about 65 wt. % ofsulfidic sulfur. Preferably, step 104 is conducted at the elevatedtemperature and pH ranges set forth in the prior paragraph. Becausewhite rot fungus also deactivates preg robbing carbon, both sulfideoxidation and preg robbing carbon deactivation (step 152) can beeffected in a single stage. In this embodiment, sulfide oxidizing and/orcarbon consuming bacteria may or may not be applied to the feed material100 along with the fungal agent.

In yet another embodiment, sulfide destruction is effected using whiterot fungus as the bioactive agent 140 and the culture media at thetemperature and pH ranges set forth above, and a different microbialagent is used to effect deactivation of the preg robbing carbon. Thepreg robbing carbon deactivation microbe is preferably bacterial but maybe fungal. Exemplary bacteria include Pseudomonas maltophilia,Pseudomonas oryzihabitans, Pseudomonas putida, Pseudomonas fluorescens,Pseudomonas stutzeri, Steptomyces setonii, Arthrobacter species,Achromobacter species, and Rhodococcus species. Because the fungalagent, during sulfide oxidation, can mobilize the gold for collection onthe preg robbing carbon, it is preferred that preg robbing carbondeactivation (step 152) be performed before sulfide oxidation (step104). In this embodiment, sulfide oxidizing bacteria may or may not beapplied to the feed material 100 along with the fungal agent.

In the above alternative embodiments, the use of an overlapping pH rangeto perform both sulfide oxidation and preg robbing carbon deactivationcan provide significant reductions in operating and capital costs andincreases in throughput compared to the two-step leaching processes setforth above.

EXPERIMENTAL

The following examples are provided to illustrate certain embodiments ofthe invention and are not to be construed as limitations on theinvention, as set forth in the appended claims. All parts andpercentages are by weight unless otherwise specified.

Example 1 Baseline Cyanidation

Three different ore samples were employed to investigate the two stagebio-oxidation-bio-treatment process. The analysis is shown in Table 1.Sample A is a flotation concentrate. Samples B and C are run-of-mine oresamples.

TABLE 1 Analysis of Ore Samples Au Ag C Preg- Sample g/t g/t (graphitic)% S % Fe % As % Robbing % A 76.1 6.00 7.03 13.30 15.30 1.12 51.8 B 4.800.24 3.00 0.69 2.25 0.62 68.9 C 2.91 0.10 2.36 3.79 6.36 1.49 80.3

Conventional bottle roll cyanidation tests were conducted using (75%minus 75 micron ore), 0.5 g/l NaCN, at a pH of 10.5, for 24 hours. Theresults presented in Table 2 show that gold extractions for each samplewere less than 22%. The sulfide and inorganic carbon contents of the oreand the low gold recovery by cyanidation indicate the samples are doublerefractory ores.

TABLE 2 Results of Straight Cyanidation Sample % Au Residue Consumption,kg/t No. Extraction g/t, Au NaCN CaO A 21.5 59.74 5.62 3.85 B 17.7 3.951.84 1.42 C 15.0 2.47 1.74 1.37

Example 2 Bio-Oxidation

The same feed samples employed in Example 1 were pre-treated usingmicrobial bio-oxidation for the treatment of the refractory sulfidiccomponent of the ore. The pretreatment consisted of grinding the ores to90% minus 200 mesh (74 μm) and forming a slurry of about 20% solids in a2 liter Erlenmeyer flask. The pH's of the slurries were adjusted toabout pH 1.5 with sulfuric acid. The chemolithotrophic bacteria used forsulfide oxidation was a mixture of equal parts Acidithiobacillusferrooxidans, Acidithiobacillus thiooxidans and Leptospirillumferrooxidans. These chemolithotrophes were grown together to form amixed culture and maintained in a medium containing about 0.5 g/l of(NH₄)₂SO₄, K₂HPO₄, MgSO₄.7H₂O, 0.1 g/l KCl and 0.01 g/l CaNO₃, 15.0 g/lFeSO₄.7H₂O, 1.0 g/l sulfur and 0.25 ml/l of Wolfe's solution. A 10% v/vmicrobial culture was added into the flask containing the pH adjustedslurry, and was agitated using an orbital shaker at 180 rpm for 14 days.At the end of microbial pre-treatment, the slurry was filtered, washedand pulped to about 33% solids for bottle roll cyanidation as outlinedin Example 1. The pregnant cyanide solution and leach residue were bothassayed for gold.

Table 3 shows that gold extraction from the ore samples pre-treated withchemolithotrophic bacteria ranged from about 71% to 81%. Thisimprovement is consistent with the liberation of gold after oxidation ofthe sulfide refractory components of the ore.

TABLE 3 Gold Extraction with Sulfide Bio-oxidation and CyanidationSample % Au Residue Consumption, kg/t No. Extraction g/t, Au NaCN CaO A81.1 14.83 1.04 0.85 B 71.1 1.42 0.55 0.25 C 73.7 0.77 0.54 0.31

Example 3 Bio-Treatment of Carbonaceous Preg Robbing Material

The same feed samples used in Examples 1 and 2 were pre-treated with onestage microbial oxidation for treatment of preg robbing carbonaceousmaterials, followed by the conventional bottle roll cyanidation asdescribed in Example 1. White rot fungus was used for deactivation ofthe carbonaceous material.

The white rot fungus, Trametes versicolor, was cultured in a mediumcontaining Kirk's medium, agar and malt extract. The 1,000 ml Kirk'ssolution contained about 10.1 grams glucose, 0.44˜0.80 grams ammoniumtartrate, 0.05 gram MnSO4.7H2O, 0.01 gram CaCl2.2H2O, 10 μml thiamine,100 μml trace minerals and 2.92 gram 2.2 dimethylsucicinate supplement.

Pretreatment of the samples included grinding the ore to 90% minus 200mesh (74 μm) and forming a slurry of 20% solids in a 2 liter Erlenmeyerflask. A 10% v/v microbial culture of Trametes versicolor was added intothe flask containing the pH 9.5 slurry, which was agitated using anorbital shaker set at 180 rpm for 14 days at ambient temperature. At theend of microbial pre-treatment, the slurry was filtered, washed andpulped to 33% solids for bottle roll cyanidation as outlined inExample 1. The pregnant cyanide solution and leach residue were bothassayed for gold.

The pH of the slurry to be leached with chemolithotrophic bacteria wasabout pH 1.5 compared to the pH used for Trametes versicolor, which wasabout pH 9.5.

Table 4 shows the gold extraction from the ore samples pre-treated withthe white rot fungus was between about 54.1 and 64.5%, which is lowerthan that treated with the chemolithotrophic bacteria in Example 2, butsignificantly higher than the gold recovery by cyanidation alone asshown in Example 1.

TABLE 4 Gold Extraction with Carbonaceous Bio-oxidation and CyanidationConsumption, Sample Bio-oxidation % Au Residue kg/t No. SpeciesExtraction g/t, Au NaCN CaO A Trametes versicolor 64.5 27.02 1.09 0.87 BTrametes versicolor 57.1 2.06 0.56 0.30 C Trametes versicolor 54.1 1.340.57 0.31

Table 4 shows that the gold extraction from the samples pre-treated withwhite rot fungus was in the range of about 54 to 65%.

Example 4 Bio-Treatment of Preg Robbing Carbonaceous Ore Followed byBio-Oxidation

A two stage pretreatment was then conducted on the three ore samplesusing the procedure outlined in Example 3 for the mitigation of pregrobbing, followed by a washing step and treatment using the process forsulfide oxidation shown in Example 2. The two-stage pre-treatment usedTrametes versicolor preg robbing deactivation followed bychemolithotrophic bacteria sulfide oxidation.

TABLE 5 Percent Gold Recovery following Biological Pre-treatments % AuResidue Consumption, Sample Extraction g/t, Au kg/t, NaCN Consumption,kg/t, CaO A 90.8 7.00 1.01 0.86 B 91.5 0.41 0.56 0.29 C 87.4 0.37 0.530.30

The results of Table 5 indicate that gold extraction after treatmentusing Trametes versicolor was relatively high.

Example 5 Bio-Oxidation and Biotreatment with Trametes versicolor

A test was performed to determine whether Trametes versicolor culturemedia (without the fungal agent) could decompose sulfides followed bydeactivation by the fungal agent of the preg robbing carbonaceouscomponents of the ore. Samples A, B, and C were conditioned with theTrametes versicolor culture media (without the fungal agent) at 30° C.for 14 days followed by bio-oxidation with Trametes versicolor atambient temperature for 7 days. Table 6 shows that approximately 95% ofgold was extracted from sample A and approximately 87% from samples Band C. By oxidizing sulfides with culture media alone at about 30° C.and about pH 9 for 28 days followed by deactivation of the preg robbingcarbon using Trametes versicolor, the same gold extraction results werealso obtained.

TABLE 6 Percent Gold Recovery using Culture Media Sulfide OxidationFollowed by Deactivation of Preg robbing Carbon using White Rot Fungus:Percent Consumption, Consumption, Au Residue g/t, kg/t kg/t Sample No.Extraction Au NaCN CaO A 95.25 3.62 0.98 0.45 B 87.00 0.62 0.41 0.34 C87.60 0.36 0.40 0.35

As can be seen from Table 6, the process produced the highest gold yieldof any test for samples A and C and the third highest for sample B. Thehighest gold yields for sample B were from two-stage sulfide oxidationand bio-treatment processes.

Summary of Results for Trametes Versicolor:

The results of the above baseline and Trametes versicolor tests ispresented below:

TABLE 7 Percent Gold Recovery following Biological Pre-treatmentsBiological Treatment % Gold Recovery Carbon Carbon Bio- Bio- treatmenttreatment Carbon Bio- by by treatment Sulfide Trametes Trametes andSulfide Bacterial versicolor versicolor Bio- Bio- with and oxidation byoxidation limited Sulfide culture with no Sulfide Bacterial media andCarbon Bio- Bio- Trametes Sample Baseline Deactivation oxidationoxidation versicolor A 21.5 81.1 64.5 90.8 95.25 B 17.7 71.1 57.1 91.587.00 C 15.0 73.7 54.1 87.4 87.60

As can be seen from Table 7, the two stage pre-treatment using Trametesversicolor yielded the highest gold recovery for sample B while theone-stage pre-treatment using the Trametes versicolor culture media(without the fungal agent) for sulfide oxidation and the Trametesversicolor culture media (with the fungal agent) for preg robbing carbondecomposition yielded the highest gold recovery for samples A and C.These results indicate that the increases in gold recovery observed frombio-oxidation and bio-treatment are cumulative and due to the reductionof both sulfide refractory and preg robbing refractory components in theore

A number of variations and modifications of the invention can be used.It would be possible to provide for some features of the inventionwithout providing others.

The present invention, in various embodiments, configurations, oraspects, includes components, methods, processes, systems and/orapparatus substantially as depicted and described herein, includingvarious embodiments, configurations, aspects, subcombinations, andsubsets thereof. Those of skill in the art will understand how to makeand use the present invention after understanding the presentdisclosure. The present invention, in various embodiments,configurations, and aspects, includes providing devices and processes inthe absence of items not depicted and/or described herein or in variousembodiments, configurations, or aspects hereof, including in the absenceof such items as may have been used in previous devices or processes,e.g., for improving performance, achieving ease and\or reducing cost ofimplementation.

The foregoing discussion of the invention has been presented forpurposes of illustration and description. The foregoing is not intendedto limit the invention to the form or forms disclosed herein. In theforegoing Detailed Description for example, various features of theinvention are grouped together in one or more embodiments,configurations, or aspects for the purpose of streamlining thedisclosure. The features of the embodiments, configurations, or aspectsof the invention may be combined in alternate embodiments,configurations, or aspects other than those discussed above. This methodof disclosure is not to be interpreted as reflecting an intention thatthe claimed invention requires more features than are expressly recitedin each claim. Rather, as the following claims reflect, inventiveaspects lie in less than all features of a single foregoing disclosedembodiment, configuration, or aspect. Thus, the following claims arehereby incorporated into this Detailed Description, with each claimstanding on its own as a separate preferred embodiment of the invention.

Moreover, though the description of the invention has includeddescription of one or more embodiments, configurations, or aspects andcertain variations and modifications, other variations, combinations,and modifications are within the scope of the invention, e.g., as may bewithin the skill and knowledge of those in the art, after understandingthe present disclosure. It is intended to obtain rights which includealternative embodiments, configurations, or aspects to the extentpermitted, including alternate, interchangeable and/or equivalentstructures, functions, ranges or steps to those claimed, whether or notsuch alternate, interchangeable and/or equivalent structures, functions,ranges or steps are disclosed herein, and without intending to publiclydedicate any patentable subject matter.

1. A method, comprising: providing a refractory gold-containing feedmaterial, the feed material comprising a preg robbing carbon-containingcomponent; inoculating the feed material with a fungal agent topassivate the preg robbing carbon-containing component, whereby at leastmost of the preg robbing ability of the carbon-containing component isdeactivated; and thereafter recovering the gold from the inoculated feedmaterial.
 2. The method of claim 1, wherein the fungal agent is at leastone of a white rot fungus and mutant thereof.
 3. The method of claim 2,wherein the fungal agent is at least one of a Coriolaceae cellularorganism and a mutant thereof.
 4. The method of claim 3, wherein thefungal agent is at least one of a Trametes species and a mutant thereof.5. The method of claim 1, wherein the inoculating step occurs at atemperature of from about 15 to about 45° C. and a pH ranging from aboutpH 5 to about pH 10, wherein the feed material comprises from about 0.1to about 5 oz/tonne gold, from about 0.3 to about 10 wt. % preg robbingcarbon-containing component, and from about 0.1 to about 15 wt. %sulfidic sulfur, and further comprising: bio-oxidizing at least about25% of the sulfidic sulfur in the feed material; and after and/or duringinoculation, contacting the feed material with nutrients for the fungalagent, the nutrients comprising a carbon source and one or more inducersto enhance production by the fungal agent of one or more selectedenzymes to cause passivation of the feed material.
 6. A method,comprising: providing a refractory gold-containing feed material, thefeed material comprising sulfidic sulfur; inoculating the feed materialwith a fungal agent to decompose at least some of the sulfidic sulfur,whereby at least a portion of the gold is released from a sulfidicmatrix; and thereafter recovering the gold from the inoculated feedmaterial.
 7. The method of claim 6, wherein the fungal agent is at leastone of white rot fungus and a mutant thereof.
 8. The method of claim 7,wherein the feed material comprises a preg robbing carbon-containingcomponent and wherein the fungal agent deactivates at least some of thepreg robbing carbon-containing component.
 9. The method of claim 8,wherein the inoculating step occurs at a temperature of from about 15 toabout 45° C. and a pH ranging from about pH 5 to about pH 10, whereinthe feed material comprises from about 0.1 to about 5 oz/tonne gold,from about 0.3 to about 10 wt. % preg robbing carbon-containingcomponent, and from about 0.1 to about 15 wt. % sulfidic sulfur, whereinat least about 25 wt. % of the sulfidic sulfur is decomposed by thefungal agent and further comprising: after and/or during inoculation,contacting the feed material with nutrients for the fungal agent, thenutrients comprising a carbon source and one or more inducers to enhanceproduction by the fungal agent of one or more selected enzymes to causedecomposition of the sulfidic sulfur.
 10. The method of claim 9, whereinthe nutrients comprise glucose, malt, and saccharomycetaceae.
 11. Amethod, comprising: providing a refractory gold-containing feedmaterial, the feed material comprising sulfidic sulfur and a pregrobbing carbon-containing component; contacting the feed material with aculture media, in the substantial absence of a microbe, to decompose atleast some of the sulfidic sulfur, whereby at least a portion of thegold is released from a sulfidic matrix; thereafter inoculating theoxidized feed material with a microbial agent and the culture media todeactivate at least some of the preg robbing carbon containingcomponent; and thereafter recovering the gold from the inoculated feedmaterial.
 12. The method of claim 11, wherein the microbial agent isselected from the group consisting essentially of white rot fungus,Pseudomonas maltophilia, Pseudomonas oryzihabitans, Pseudomonas putida,Pseudomonas fluorescens, Pseudomonas stutzeri, Steptomyces setonii,Arthrobacter species, Achromobacter species, and Rhodococcus species,and mutants and consortia thereof.
 13. The method of claim 11, whereinthe fungal agent deactivates at least some of the preg robbingcarbon-containing component.
 14. The method of claim 13, wherein thecontacting step occurs at elevated temperature, wherein the inoculatingstep occurs at a temperature of from about 15 to about 45° C., whereinthe contacting and inoculating steps occur at a pH ranging from about pH5 to about pH 10, wherein the feed material comprises from about 0.1 toabout 5 oz/tonne gold, from about 0.3 to about 10 wt. % preg robbingcarbon-containing component, and from about 0.1 to about 15 wt. %sulfidic sulfur, wherein at least about 25 wt. % of the sulfidic sulfuris decomposed by the contacting step and wherein the culture mediacomprises a carbon source and one or more inducers to enhance productionby the microbial agent of one or more selected enzymes to causedecomposition of the preg robbing carbonaceous component.
 15. The methodof claim 11, wherein the culture media comprises glucose, malt, andsaccharomycetaceae.
 16. A method, comprising: providing a refractorygold-containing feed material, the feed material comprising a pregrobbing carbon-containing component; inoculating the feed material witha fungal agent other than a Phanerochaete cellular organism todeactivate the preg robbing carbon-containing component, whereby atleast most of the preg robbing ability of the carbon-containingcomponent is deactivated; and thereafter recovering the gold from theinoculated feed material.
 17. The method of claim 16, wherein the fungalagent is at least one of a white rot fungus and mutant thereof.
 18. Themethod of claim 17, wherein the fungal agent is at least one of aCoriolaceae cellular organism and a mutant thereof.
 19. The method ofclaim 18, wherein the fungal agent is at last one of a Trametes speciesand a mutant thereof.
 20. The method of claim 16, wherein theinoculating step occurs at a temperature of from about 15 to about 45°C. and a pH ranging from about pH 5 to about pH 10, wherein the feedmaterial comprises from about 0.1 to about 5 oz/tonne gold, from about0.3 to about 10 wt. % preg robbing carbon-containing component, and fromabout 0.1 to about 15 wt. % sulfidic sulfur, and further comprising:bio-oxidizing at least about 25% of the sulfidic sulfur in the feedmaterial; and after and/or during inoculation, contacting the feedmaterial with nutrients for the fungal agent, the nutrients comprising acarbon source and one or more inducers to enhance production by thefungal agent of one or more selected enzymes to cause passivation of thefeed material.